The invention concerns a process and a press for manufacturing laminated plastic cards, such as check guarantee cards, credit cards and the like of several films to be pressed together, having two compression plates which are heatable and/or coolable and which accommodate the films to be pressed in the compression slot, whereby at least one compression pad and a pressure plate are arranged between the films and at least one compression plate.
To the extent that plastic cards are presently being discussed, any desired laminated cards are to be understood by this in connection with which the electronic components such as data carriers, magnetic strips or chips, are arranged either in the outer surfaces or, as with the so-called non-contacting cards, are incorporated into the interior. The cards moreover comprise of at least two sheets as cover sheets and at least one sheet as middle sheet. These films are brought, in one or more successive heat presses, by the action of pressure and heat, to the melting temperature required for the lamination process and subsequently cooled down in at least one cold press until the individual cards can be stamped out of the laminate.
In manufacturing such plastic cards, the exact control of the process temperature during the pressing process is of particular significance. Not only must the correct melting temperature be reached in the core of the individual films in order to guarantee the lamination process, but it is also necessary to observe the temperature gradient.
An excessively rapid increase in temperature can generate bubbles in the plastic. In contrast, with an excessively rapid cooling, in particular in connection with a chilling of the hot films on the cold compression plates of the cold press, the formation of cracks can occur.
For this reason, frequently so-called compression pads are used which are embedded between the film package and the compression plates. They prevent a local overheating in the hot press as well as chilling in the cold press because they ensure a uniform heat transfer. In addition to this, thickness tolerances in the compression material and the compression plates are also balanced.
Another important requirement is provided in that the surface of the plastic card must be constructed absolutely flat, with bright luster and without faults. This is attained in that the films to be laminated are in any given case grasped between so-called pressure plates. These pressure plates are made of high luster polished high grade steel sheets of about 0.5 mm thickness, although in the future, perhaps other materials can be used as well. These pressure plates insure that the laminate receives the desired smooth surface. Selectively, contoured pressure plates can also be used if the plastic cards are supposed to have a corresponding surface structure.
In order to increase productivity, use of so-called multiple stage presses in which a great number of film stacks stacked one above the other can be laminated at the same time is known. Here of course a certain temperature drop between the outside lying heated films and the core area must be tolerated, which is disadvantageous for exact adherence to the processing temperature.
In addition, these multiple stage presses require a great number of the previously mentioned pressure plates which causes considerable costs due to their high luster polished finish.
Not in the least, multiple stage presses also require a relatively long cycle time until the laminates are heated up and cooled down again. It is necessary to allow for about 45 minutes until a ready laminate can be further processed.
In addition, manufacturing laminates individually is also known through DE 44 41 552. This means that only so many individual films are fed to the presses as are necessary for one laminated individual film. In this way, one can operate with basically shorter cycle times in the seconds range and also control the temperature course in the films more precisely. Moreover, the equipment expenditure is clearly lower than with a multiple stage press.
Proceeding from this, underlying the present invention is the objective of further perfecting the last described short cycle process for plastic card laminates, especially to simplify the process sequence and to increase the cycle speed.
This object is accomplished in accordance with the invention in that the compression pads are no longer applied as previously known as a loose intermediate layer or placed under the stack of films, but in that they are held (rigidly or displaceably) on the press.
In this way, aligning and applying the compression pads in the positioning station where the stack of films is built up, as well as dismounting the compression pad in the removal station where the finished laminates are taken out are dispensed with. The sequence of operations is in this way simpler and shorter, and a source of defects is eliminated because during application of the compression pad, there exists the risk of moving the films situated underneath. The process consequently permits the manufacture of laminated plastic cards with a short cycle time process in the seconds range.
In refining the invention, keeping the compression pad under tensile stress (at least the compression pad arranged on the upper compression plate) is recommended so that it does not sag, but rather is held in place on the compression plate over as large an area as possible and consequently also assumes their heating or cooling temperature.
Basically, it would also be possible to glue the compression pad to its respective compression plate. But then changing, which is necessary now and then, would be more expensive than using a fastening device which is easily accessible on the exterior, meaning that it can be mounted on the periphery of the compression plate.
Appropriately, the compression pad projects on at least two edges lying opposite each other laterally beyond the compression plate and is fixed there under tensile stress, in particular unilaterally connected to a fastening device. Here the projecting edges of the compression pad can also be more or less bent backward, thus in the direction opposite to the compression slot, so that the attachment of the compression pad in relation to the compression plate is likewise shifted in the direction opposite to the compression slot.
Generally it suffices if the one projecting edge of the compression pad is fixed alongside the compression plate, while the opposite edge is mounted in the fastening device. This fastening device can be constructed in the form of a clamp which is adjustably mounted somewhat parallel to the contact surface of the associated compression plate on it.
The compression pad is preferably a rubber-elastic band with a thickness in the order of magnitude of 1 mm. In order for it to withstand the desired bracing, it can have a fabric in the interior which is coated with plastic on both sides.
With respect to the process, it is especially appropriate to use the separation surface for the transport of films to the individual treatment stations, especially such that pressure plates are used which protrude on the edge opposite the films on two opposite sides and are picked up on this protruding edge by the transport device.
At the same time, the pressure plates can easily be pressed together by the transport device in order to maintain the exact fitting position of the individual films prior to lamination. Alternatively, the pressure plates are only held in their relative position in relation to one another by fixation pins traversing them.
Basically, an endless circulating transport device can be used which passes through all processing stations. Usually it is more economical, however, to construct the transport device such that it always travels back and forth only between two adjacent processing stations.
So that the laminate can easily be taken out of the removal station, especially in order to cancel its adhesion to the pressure plates, it is recommended that the pressure plate be somewhat bent with the laminate in the sense of an even arching. After this at least the one presser plate can easily be lifted from the laminate.